In her book Breaking the Abortion Deadlock: From Choice to Consent, sociologist Eileen McDonagh argued that pro-choice people should move the debate from being about choice to consent. In other words, instead of arguing a woman has a "right to choose" abortion, they should be arguing that an embryo only has the right to a woman's uterus if she grants consent to the uterus, and only if consent is ongoing. She argued that sex doesn't make a woman pregnant, sex only creates the embryo, and it's the embryo that makes the woman pregnant. Since the embryo occupies the woman's uterus against her will, the embryo is essentially a rapist, or a parasite (or perhaps one of the aliens from Alien). Since the embryo is essentially a rapist, the state has an obligation to protect her from this invader in the same way the state would use the police to protect her from an actual rapist.
That's the thesis of her book, essentially. McDonagh has succeeded to some degree in changing the abortion debate to be about consent. I don't encounter this argument when I'm talking to a pro-abortion-choice advocate in person. But I occasionally encounter this argument in on-line discussions. It doesn't hold up to scrutiny, and it's not an argument that is seriously defended by most pro-abortion-choice people. It's more of an argument pro-abortion-choice people keep in their quiver as a backup.
The argument fails for a few reasons, mainly because it has a wrong idea of where to place responsibility for the pregnancy. It's true that sex creates the embryo, but what is missed is not simply that the embryo is too young to have any rational idea of what is going on so he/she is not morally responsible for implanting in the uterus, but the embryo also is not causally responsible for implanting in the uterus. The woman's body is. Once the embryo is conceived from the sperm and the ovum, tiny hairs in the fallopian tube, called cilia, then pick up the newly conceived embryo and transport it into the uterus, where it then implants. It is the act of sex, itself, that not only conceives the embryo but also causes the embryo to implant in the uterus since it starts a chain reaction of causes and effects that results in pregnancy. Any woman who consensually engages in sex is responsible, morally and causally, for her pregnancy (of course, the man is responsible, too, but I am focusing on the woman for the purposes of this discussion). Since she engages in an act that is intrinsically ordered toward procreation, she is, then, morally responsible for caring for any embryo that results from this union.
On top of tacitly granting consent to the use of her uterus by virtue of the fact she consented to the act that created the embryo and placed the embryo in a state of dependence upon her, this consent cannot be revoked. If the only way to remove someone from your property is to kill them, you cannot evict them. By way of analogy, if I allow someone the use of my house, I can revoke consent at any time. However, if I have granted that person consent to use my storm cellar during a tornado, I cannot then revoke consent until the tornado is gone and there is no danger. Even the idea of tacit consent can be seen here. Suppose "Weird Al" Yankovic's in town. I go to where he is appearing, then I drug his drink and take him back to my home, refusing to let him leave until he signs all of my CD's. But suppose I live in Kansas and in the midst of trying to get his autograph, a tornado touches down near my house. I can't, then, turn him out and say "tough luck, pal. You refused to polka with me, so my storm cellar, my choice." I now have a tacit obligation to protect him in my storm cellar because I have placed him in a state of dependence on me for protection.
Another argument sometimes invoked to make this point is if you get into a car and get into an accident, you consented to drive but you did not consent to being in an accident. The doctor will still heal the person, even though they consented to get behind the wheel.
This is, of course, true. But driving is not an act that intrinsically leads to getting in an accident in the same way that sex intrinsically leads to getting pregnant. If everything works as it is intended, then having sex will conceive a child. However, in driving, getting in an accident is an abuse of the intended function of the car. The intended function is to transport people and objects.
To reiterate, this argument is not a very good one. It is also easy to show why the argument doesn't work. It requires denial of the metaphysical reality of cause and effect, namely that sex causes pregnancy; it doesn't just cause the embryo. The embryo would not exist if the man and woman did not have sex in the first place.